Vacuum-type circuit interrupter with contact material containing a minor percentage of beryllium

ABSTRACT

A vacuum-type circuit interrupter comprising a pair of contacts relatively movable into and out of engagement, the contacts having circuit-making and -breaking regions formed of an alloy consisting essentially of copper-beryllium and bismuth, the beryllium being present in a quantity of between 2 percent and 19 percent by weight of the copper-beryllium and the bismuth being present in a quantity of less than about 5 percent by weight of the total alloy but in a sufficient quantity to inhibit contact welding.

United States Patent Inventors Appl. No

Filed Patented Assignee Fordyce H. Horn, deceased late 01 Schenectady County. N.Y. (by Helen W. Horn, executrix);

Joseph W. Porter; Joseph L. Talento, both of Media, Pa.

Dec. 29, 1969 June 22, 1971 General Electric Company Continuation-impart of application Ser. No.

647,646, June 21, 1967, now abandoned.

VACUUM-TYPE CIRCUIT INTERRUPTER WITH CONTACT MATERIAL CONTAINING A MINOR PERCENTAGE OF BERYLLIUM [56] References Cited UNITED STATES PATENTS 3,014,108 12/1961 Cobine etal ZOO/144B 3,140,373 7/1964 Horn 200/144B 3,234,351 2/1966 Hebb 200/144 B 3,246,979 4/1966 Lafferty et a1. 200/144 BX 3,497,652 2/1970 Horn et a1. 200/144 B FOREIGN PATENTS 1,025,943 4/1966 Great Britain 200/144 B I 1,025,944 4/1966 Great Britain 200/144 8 6 Claims, 2 Drawing Figs.

US. Cl 200/144, 200/166 Int. Cl H0111 33/66 Field 01 Search 200/144 B, 166 C Primary Examiner-Robert S. Macon Attornys.1. Wesley Haubner, William Freedman, Frank Lo Neuhauser, Oscar B, Waddell and Joseph B. Forman ABSTRACT: A vacuum-type circuit interrupter comprising a pair of contacts relatively movable into and out of engagement, the contacts having circuit-making and -breaking regions formed of an alloy consisting essentially of copper-beryllium and bismuth, the beryllium being present in a quantity of between 2 percent and 19 percent by weight of the copperberyllium and the bismuth being present in a quantity of less than about 5 percent by weight of the total alloy but in a sufficient quantity to inhibit contact welding.

VACUUM-TYPE CIRCUIT INTERRUPTER WITH CONTACT MATERIAL CONTAINING A MINOR PERCENTAGE OF BERYLLIUM This application is a continuation-in-part of application Ser. No. 647,646, filed June 21, 1967, now abandoned.

BACKGROUND OF THE INVENTION This invention relates to a vacuum-type circuit interrupter and, more particularly, to contact structure for such an interrupter.

In U.S. Pat. No. 3,246,979-Lafferty et al., assigned to the assignee of the present invention, it is proposed that the contacts of a vacuum interrupter be formed of analloy consisting essentially of a majorconstituent which is a good-conductivity, nonrefractory metal and a minor constituent which is a metal having a lower freezing temperature than the major constituent and little or no solid-state solubility in the major constituent, the minor constituent being present in a quantity of a few percent or less by weight of the alloy. Examples of such alloys are copper-bismuth, copper-lead, copper-tellurium, silver-bismuth, silver-lead, and silver-tellurium, each alloy containing a few percent or less by weight of the second mentioned, or minor, constituent. In referring to a few percent by weight, we mean less than about percent by weight.

Vacuum interrupters having contacts of these alloys can interrupt high inductive currents (e.g., in excess of 8,000 amperes symmetrical r.m.s.) at rated voltage, can carry and close against such currents without producing objectionable contact-welds, and can successfully withstand impulse crest voltages of at least 95 kv. and continuous 60-cycle voltages of at least 36 kv. r.m.s. when their contacts are fully separated. These voltages are those which indoor oilless circuit breakers rated at 7.2 kv. and 13.8 kv. must be capable of withstanding if they are to meet therequirements of the National Electrical Manufacturers Association (NEMA) Standards for Power Circuit Breakers, Publication SG4-1954, Mar. 1954, revised Nov. 1955, Part 2, page 5.

For higher voltage ratings and for certain switching operations, such as capacitance switching, even more difficult dielectric strength requirements are imposed upon the interrupter. One severe measure of an interrupter's ability to meet these more difficult dielectric strength requirements is its ability to withstand a high transient voltage immediately following a contact-separating operation which fractures a weld between the contacts, especially the type of weld formed by closing on several thousand amperes or more of current.

Although entirely satisfactory for many circuit applications, vacuum interrupters having their contact-making and -breaking regions consisting of copper-bismuth, copper-lead or the other materials disclosed in the aforesaid Lafferty et al. patent have not been able to meet this latter test as well as might be desired. It appears that fracture of the weld between the contacts leaves surface irregularities that detract from the ability of the intercontact gap to withstand the high transient voltage.

SUMMARY An object of the present invention is to provide a vacuum interrupter that has improved ability to withstand high voltages immediately following a contact-separating operation that fractures a weld between the contacts.

Another object is to consistently achieve a high dielectric strength between the contacts immediately following contact separation which follows closing on high inrush currents.

Another object is to provide a vacuum interrupter capable of performing as setforth in the immediately preceding paragraphs and also capable l of interrupting high inductive cur rents of 8,000 or more amperes r.m.s. symmetrical, (2) of being free from objectionable contact welding, and (3) of meeting the high dielectric strength requirements imposed by conventional standards at rated circuit voltages of 14.4 kv. and higher. (The above NEMA Standards require that an oilless circuit breaker rated at 14.4 kv. be capable of withstanding kv. peak impulse voltage and 50 kv. r.m.s. continuous voltage.)

In carrying out our invention in one form we provide the vacuum interrupter with contacts having their circuit-making and -breaking regions made of an alloy of copper-beryllium and bismuth. The beryllium is present in a quantity of between 2 percent and 19 percent by weight of the copper-beryllium, and the bismuth is present in a quantity of less than about 5 per cent by weight of the total alloy but in a sufficient quantity to inhibit contact welding. In a preferred form of the invention, the beryllium is present in a quantity of between 5 and 9 percent by weight of the copper-beryllium.

BRIEF DESCRIPTION OF DRAWINGS For a better understanding of our invention, reference may be had to the following description taken in conjunction with the accompanying drawings, wherein: 7

FIG. I is a sectional view of a vacuum-type circuit interrupter embodying one form of our invention.

FIG. 2 is an enlarged perspective view of one of the contacts of the interrupter of FIG. I.

DESCRIPTION OF PREFERRED EMBODIMENT Referring now to the interrupter of FIG. 1, there is shown a highly evacuated envelope 10 comprising a casing 11 of a suitable insulating material, such as glass, and a pair of metallic end caps 12 and 13, closing off the ends of the casing. Suitable seals 14 are provided between the end caps and the casing to render the envelope l0 vacuumtight. The normal pressure within the envelope 10 under static conditions is lower than l0 mm. of mercury so that a reasonable assurance is had that the mean free path for electrons will be longer than the potential breakdown paths in the envelope.

The internal insulating surfaces of casing 11 are protected from the condensation of arc-generated metal vapors thereon by means of a tubular metallic'shield l5 suitably supported on the casing 11 and preferably isolated from both end caps 12 and 13. This shield acts in a well known manner to intercept arc-generated metallic vapors before they can reach the casing 11.

Located within the envelope 10 is a pair of separable contacts 17 and 18, shown in their engaged or closed-circuit position. The upper contact 17 is a stationary contact suitably attached to a conductive rod 17a, which at its upper end is united to the upper end cap 12. The lower contact 18 is a movable contact joined to a conductive operating rod 18a which is suitably mounted for vertical movement. Downward motion of the contact 18 separates the contacts and opens the interrupter, whereas return movement of contact 18 reengages the contacts and thus closes the interrupter. A typical gap length hen the contacts are fully open is about one-half inch. The operating rod 18a projects through an opening in the lower end cap 13, and a flexible metallic bellows 20 provides a seal about the rod 18a to allow for vertical movement of the rod without impairing the vacuum inside the envelope 10. As shown in FIG. 1, the bellows 20 is secured in sealed relationship at its respective opposite ends to the operating rod 18a and the lower end cap 13.

All of the internal parts of the interrupter are substantially free of surface contaminants. These clean surfaces are obtained by suitably processing the interrupter, as by baking it out during its evacuation. A typical bakeout temperature is 400 C. In addition, the contacts 17 and 18 are effectively freed of gases absorbed internally of the contact body so as to preclude evolution of these gases during high current arcing. The manner in which these internal gases are removed will be referred to in more detail hereinafter.

Although our invention is not limited to any particular contact configuration, we prefer to use the contact configuration disclosed and claimed in US. Pat. No. 2,949,520, Schneider, assigned to the assignee of the present invention. Accordingly,

each contact is of a disc shape and has one of its major surfaces facing the other contact. The central region of each contact is formed with a recess 29 in this major surface and an annular circuit-making and circuit breaking area 30 surrounds this recess. These annular circuit-making and -breaking areas 30 abut against each other when the contacts are in their closed position of FIG. 1, and are of such a diameter that the current flowing through the closed contacts follows a loopshaped path L, as is indicated by the dotted lines of FIG. 1. Current flowing through this loop-shaped path has a magnetic effect which acts in a known manner to lengthen the loop. As a result, when the contacts are separated to form an are between the areas 30, the magnetic effect of the current flowing through the path L will impel the arc radially outward.

As the arc terminals move toward the outer periphery of the discs 17 and 18, the arc is subjected to a circumferentially acting magnetic force that tends to cause the arc to move circuthferentially about the central axes of the discs. This circumferentially acting magnetic force is preferably produced by a series of slots 32 provided in the discs and extending from the outer periphery of the discs radially inward by generally spiral paths, as is shown in FlG. 2. These slots 32 correspond to similarly designated slots in the aforementioned Schneider patent and thus, force the current flowing to or from an arc terminal located at substantially any angular point on the outer peripheral region of the disc to follow a path that has a net component extending generally tangentially with respect to the periphery in the vicinity of the arc. This tangential configuration of the current path results in the development of a net tangential force component, which tends to drive the arc in a circumferential direction about the contacts. In certain cases, the arc may divide into a series of parallel arcs, and these parallel arcs move rapidly about the contact surface in a manner similar to that described hereinabove.

One of the problems that the present invention is concerned with is providing a single-break vacuum interrupter of the general type described up to this point that is capable of meeting the conventional NEMA specification for an oilless circuit breaker having a voltage rating of at least 14.4 kv. and an interrupting rating of at'least 8,000 amperes r.m.s. symmetrical and is also capable of consistently withstanding high transient voltages applied immediately following a contact-separating operation that fractures a weld between the contacts. In referring to high transient voltages, we are referring to those typically encountered in switching and interrupting circuits rated at 14.4 kv. and higher; and in referring to a weld between the contacts, we are particularly concerned with those welds such as might be formed when an are carrying inrush currents of several thousand amperes is developed during contact closing.

We have found that these requirements can be met by forming the circuit-making and circuit breaking portions 30 of the vacuum interrupter contacts of an alloy consisting of copperberyllium and bismuth, the beryllium being present in a quantity of between 2 and 19 percent by weight of the copperberyllium and the bismuth being present in a quantity of a few percent or less by weight of the total alloy. A specific alloy which has shown'exceptional ability to meet these requirements is a copper-beryllium-bismuth allow consisting essentially of copper, beryllium in a quantity of 7 per cent by weight of the copper-beryllium, and bismuth in a quantity of 1 percent by weight of the total alloy. This material is referred to hereinafter as Cu-Be-Bi (7 percent Be).

The material of the prior art found most satisfactory for the contacts of the vacuum interrupter has been an alloy of copper-bismuth consisting of copper and a few percent or less of bismuth by weight, e.g., 0.5 percent. A vacuum interrupter with contacts of this material can meet the conventional NEMA specification for oilless circuit breakers rated at 14.4 kv. and 8,000 amperes r.m.s. interrupting current, but it has not been able to withstand as consistently as might be desired a high voltage transient applied following a contactseparating operation which fractures a weld between the contacts.

To provide a measure of this dielectric strength after weld fracture, we have conducted an extensive series of the following tests on vacuum interrupters'with different contact materials, but otherwise of comparable design. First, the contacts of a given vacuum interrupter were driven together against currents sufficiently high to produce a weld between the contacts; and then the contacts were opened under no-current conditions to fracture the weld, and the open gap was stressed with a voltage of a waveform simulating a switching surge. This voltage had an available crest value high enough to break down the gap each time it was applied, and the instantaneous voltage at the instant of breakdown was recorded. The available crest value was 230 kv., and the rate of rise was such that this crest would be reached in microseconds in the absence of a breakdown. The current against which the contacts were closed was the same in each test, being 3,000 amperes peak current. These test results were plotted on probability paper, with the voltage stress required for breakdown being plotted against the probability of breakdown. For given probabilities of breakdown, it was found that with contacts of Cu-Be-Bi (7 percent Be) the intercontact gap could withstand a voltage stress greater than 300 percent of that withstandable by a gap between contacts of Cu-Bi (0.5 percent Bi). For example, a voltage stress of kv./in. produced a 50 percent probability of breakdown with the Cu-Bi contacts, but 360 kv./in. (or about 340 percent of the Cu-Bi voltage stress) was needed to produce the same probability of breakdown with the Cu-Be-Bi (7 percent Be) contacts. It will therefore be apparent that the Cu-Be-Bi (7 percent Be) contacts exhibit greatly improved performance over Cu-Bi (0.5 percent Bi) from the standpoint of dielectric strength after weld fracture.

Metallographic studies have been made in an effort to determine the structural differences that are responsible for the improved performance of the copper-beryllium-bismuth alloys containing 2 to 19 percent beryllium by eight of the copper-beryllium. When the amount of beryllium is reduced below 2 percent, the grains of the alloy are quite large and most of the beryllium is in solid solution with the copper. The bismuth forms a thin film around each of these grains and has a marked embrittling effect on the alloy. For higher quantities of beryllium, considerable amounts of beryllium are present with copper as the eutectoid composition (94 Cu-6 Be), which appears as a fine dispersion throughout the grains and the grain boundaries. The presence of this fine dispersion produces a better distribution of the bismuth inside the grains and greatly reduces bismuth segregation at the grain boundaries. The bismuth, while still being available as a weld-inhibiting agent, has much less of an embrittling effect on the parent alloy, and the result is improved mechanical strength and ductility. These improvements in mechanical strength and ductility are believed to contribute to improved dielectric strength because they reduce the possibility that discrete particles of metal will be pulled out of the opposite contact when the contacts are separated following such minor contact welding as does occur. Moreover, even though the bismuth is not concentrated at the grain boundary in the parent alloy, it is still present distributed throughout the grain structure and is available to segregate in the weld zone caused by arcing. This segregated bismuth weakens the weld by forming a weak interface along which the contacts can easily separate when subsequently opened. This further reduces the possibility that a discrete particle of metal will be pulled out of the opposite contact along a grain boundary. By reducing this possibility, we are able to maintain contact surfaces of greater smoothness with fewer protuberances of a size that would encourage a dielectric breakdown.

When the quantity of beryllium is increased beyond about 11.5 percent by weight of the copper-beryllium, some of the interrnetallic compound phase Be Cu is formed. The intermetallic compound is a very brittle material, and its presence increases the brittleness of the overall contact material. It appears that about 19 percent beryllium can be added to the copper before excessive brittleness occurs. Despite the presence of the intermetallic phase when beryllium is present in amounts between l 1.5 and 19 percent, there appears to be sufficient B phaseremaining to adequately offset the brittleness of the intermetallic phase. Amounts of beryllium greater than about l9 percent impart so much brittleness that it becomes impractical to machine the material into contacts or to subject them to closing impacts without producing cracking. 7

Contacts of copper-beryllium-bismuth alloy have also shown an exceptional resistance to cold welding, i.e., welding together under the influence of high pressure forcing'the contacts together with no arcing between the contacts. For example, a series of tests have been made in which contacts of different materials have been forced together'with 3,000 pounds of force, and then separated to fracture any weld present between them. The force required to separate them is measured. With contacts of the plain copper-bismuth Cu-Bi (0.5 percent Bi) referred to hereinabove, welds requiring approximately 80 pounds of force'for their fracture were developed. With contacts formed of Cu-Be-Bi containing 3 to 19 weight percent of beryllium, substantially no welds were formed. This freedom from substantial cold-welding is a significant advantage not only because it reduces the force necessary to separate the contacts but also because it reduces the likelihood that protuberances will be formed at the fractured weld which could impair the dielectric strength.

As pointed out hereinabove, another condition that can lead to contact welding is that accompanying closing the circuit interrupter against heavy currentsQWhen the contacts are driven into closed position, they often bounce apart a short distance immediately after initial impact and then rebound toward each other, aided by the closing force applied to the movable contact. An arc is drawn when the contacts first bounce apart, and this arc melts adjacent surface portions of the contacts so that when they rcengage, a molten film is present at the interface. When arcing ceases following reengagement, the energy input into the contact interface drops sharply, and the film at the interface thus quickly cools to a solid state. The result is the formation of a weld between the two contacts. The higher the arcing current, the larger the surface area that will be covered by the molten film and hence the larger and stronger the weld ordinarily will be. The welds formed under these conditions will be referred to as hot welds.

For determining the relative strengths of welds that are formed under these conditions, clean contacts of various materials were driven together under high current arcing conditions, and the force required for their subsequent separation was measured. To prevent the formation of oxide or other films on the contacts, these tests ere run in an inert atmosphere of argon, which provides ambient conditions with respect to oxidation closely simulating those present under high vacuum conditions. With contacts of plain copper, an opening force of 5,000 pounds was typically required to fracture the weld and separate the contacts; with contacts of Cu- Bi (0.5 percent Bi), an opening force of l25200 pounds was typically required; with Cu-Be-Bi (7 percent Be) an opening force of only 0 to 10 pounds was typically required.

This greatly improved resistance to the formation of both cold welds and hot welds is an unexpected property of the contacts of coppenberyllium-bismuth having a beryllium content in the vicinity of the preferred 7 percent by weight of the copper-beryllium.

Although we have described the invention specifically with respect to contacts of a copper-base alloy containing bismuth as a weld-inhibiting agent, the invention in its broader aspects is also considered to be applicable to copper-base alloy contacts which contain the other weld-inhibiting agents of the aforesaid Lafferty et al. patent. For example, copper-base alloy contacts with lead or tellurium can be dielectrically improved by adding beryllium, in an amount of 2 to 19 percent by weight of the copper-beryllium alloy. in each of these materials, the weld-inhibiting agent is substantially insoluble in the solid state in both copper and beryllium and has a lower 1" improved dielectrically by including beryllium in approxi- "f mately'the same percentage'by 'weig h't' of'the silver-beryllium alloy as used in the copper-base alloys, i.e., 2 to 19 percent.

Similarly, a nickel-base alloy with a bismuth weld inhibitor can be improved dielectrically by including beryllium in approximately 2 to l 1.5 percent by weightof the nickel-beryllium alw "in referring to weld-inhibiting agents that are. substantially insoluble in the'othe r constituents in the solid state, we are referring to weld inhibiting metals that have a solid-state solubility in the other constituents of less than about 2 percent by weight of the alloy considered at the eutectic temperature of said alloy or the freezing temperature of the minor constituent if there is no eutectic.

in referring to a few percent by weight of the total alloy, we mean less than about 5 percent by weight of the total alloy. In each of the materials, a sufficient quantity of the weld-inhibiting metal is present to effectively inhibit contact welding.

In preparing these contact materials, each separate constituent first should be suitably processed to free it of sorbed gases and other contaminants, as, for example, by the zonerefining process described in U.S. Pat. No. 3,234,35 l-Hebb, assigned to the assigneeof the present invention. The constituents are then melted and appropriately mixed together while they are in the liquid state, after which the temperature is lowered to cause the constituents to solidify and form the solid alloy.

Although the contacts 17 and 18 may be made entirely of the contact materials of our invention,'it is to be understood that it is generally sufficient that only the circuit-making and breaking regions 30 be formed of these materials. The remainder of each contact may be formed of another material suitable for interrupting high currents and having good dielectric strength properties, e.g., copper.

While we have shown and described particular embodiments of our invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from our invention in its broader aspects; and we, therefore, intend in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of our invention.

What is claimed as new and desired to secure by Letters Patent of the United States is:

l. A vacuum-type electric circuit interrupter comprising:

a. an envelope evacuated to a pressure of l0 mm. of mercury or less,

b. a pair of contacts within said envelope relatively movable into and out of engagement,

c. said contacts being substantially free of absorbed gases and surface contaminants,

d. at least one of said contacts having circuit-making and breaking regions formed of an alloy consisting essentially of copper-beryllium and bismuth,

e. the beryllium being present in a quantity of between 2 and 19 percent by weight of the copper-beryllium, and

f. the bismuth being present in a quantity of less than about 5 percent by weight of the total alloy and in sufficient quantity to inhibit contact welding, and being distributed throughout said alloy.

2. The vacuum-type circuit interrupter of claim 1 in which the beryllium is present in a quantity of between 5 and 9 percent by weight of the copper-beryllium.

3. The vacuum-type circuit interrupter of claim 1 in which the beryllium is present in a quantity of substantially 7 percent by weight of the copper-beryllium.

4. A vacuum-type electric circuit interrupter comprising:

a. an envelope evacuated to a pressure of 10 mm. of mercury or less, r

b. a pair of contacts within said envelope relatively movable into and out of engagement,

c. said contacts being substantially free of absorbed gases and surface contaminants,

d. at least one of said contacts having circuit-making and breaking regions formed of an alloy consisting essentially of copper-beryllium and a weld-inhibiting metal having substantially no solid-state solubility in copper or beryllium and having an effective freezing temperature below that of copper-beryllium,

e. the beryllium being present in a quantity of between 2 and 19 percent by weight of the copper-beryllium, and

f. the weld-inhibiting metal being present in a quantity of less than about 5 percent by weight of the total alloy and in sufficient quantity to inhibit contact-welding, and being distributed throughout said alloy.

, 5. A vacuum-type electric circuit interrupter comprising:

a. an envelope evacuated to a pressure of IO mm. of mercury or less,

b. a pair of contacts within said envelope relatively movable into and out of engagement,

c. said contacts being substantially free of absorbed gases and surface contaminants d. at least one of said contacts having circuit-making and breaking regions formed of an alloy consisting essentially of a good-conductivity metal alloyed with beryllium and bismuth, the good conductivity metal being one in which bismuth has substantially no solid-state solubility,

. the beryllium being present in a quantity of between 2 and 19 percent by weight of the good-conductivity metalberyllium alloy but in a quantity sufficiently low that a phase of said latter alloy other than intermetallic compound is present-to impart effective machinability and resistance to cracking on closing impact,

f. the bismuth being present in a quantity of less than about 5 percent by weight of the total alloy and in sufficient quantity to inhibit contact welding, and being distributed through said alloy.

6. A vacuum-type electric circuit interrupter comprising:

. a. an envelope evacuated to a pressure of 10" mm. of mere. the beryllium being present in a quantity of between 2 I and 19 percent by weight of the good conductivity metal beryllium alloy but in a quantity sufficiently low that a phase of said latter alloy other than intermetallic compound is present to impart effective machinability and resistance to cracking on closing impact,

f. the weld-inhibiting metal being present in a quantity of less than about 5 percent by weight of the total alloy and in sufficient quantity to inhibit contact welding, and being distributed throughout said alloy. 

1. A vacuum-type electric circuit interrupter comprising: a. an envelope evacuated to a pressure of 10 4 mm. of mercury or less, b. a pair of contacts within said envelope relatively movable into and out of engagement, c. said contacts being substantially free of absorbed gases and surface contaminants, d. at least one of said contacts having circuit-making and breaking regions formed of an alloy consisting essentially of copper-beryllium and bismuth, e. the beryllium being present in a quantity of between 2 and 19 percent by weight of the copper-beryllium, and f. the bismuth being present in a quantity of less than about 5 percent by weight of the total alloy and in sufficient quantity to inhibit contact welding, and being distributed throughout said alloy.
 2. The vacuum-type circuit interrupter of claim 1 in which the beryllium is present in a quantity of between 5 and 9 percent by weight of the copper-beryllium.
 3. The vacuum-type circuit interrupter of claim 1 in which the beryllium is present in a quantity of substantially 7 percent by weight of the copper-beryllium.
 4. A vacuum-type electric circuit interrupter comprising: a. an envelope evacuated to a pressure of 10 4 mm. of mercury or less, b. a pair of contacts within said envelope relatively movable into and out of engagement, c. said contacts being substantially free of absorbed gases and surface contaminants, d. at least one of said contacts having circuit-making and -breaking regions formed of an alloy consisting essentially of copper-beryllium and a weld-inhibiting metal having substantially no solid-state solubility in copper or beryllium and having an effective freezing temperature below that of copper-beryllium, e. the beryllium being present in a quantity of between 2 and 19 percent by weight of the copper-beryllium, and f. the weld-inhibiting metal being present in a quantity of less than about 5 percent by weight of the total alloy and in sufficient quantity to inhibit contact-welding, and being distributed throughout said alloy.
 5. A vacuum-type electric circuit interrupter comprising: a. an envelope evacuated to a pressure of 10 4 mm. of mercury or less, b. a pair of contacts within said envelope relatively movable into and out of engagement, c. said contacts being substantially free of absorbed gases and surface contaminants d. at least one of said contacts having circuit-making and -breaking regions formed of an alloy consisting essentially of a good-conductivity metal alloyed with beryllium and bismuth, the good conductivity metal being one in which bismuth has substantially no solid-state solubility, e. the beryllium being present in a quantity of between 2 and 19 percent by weight of the good-conductivity metal-beryllium alloy but in a quantity sufficiently low that a phase of said latter alloy other than intermetallic compound is present to impart effective machinability and resistance to cracking on closing impact, f. the bismuth being present in a quantity of less than about 5 percent by weight of the total alloy and in sufficient quantity to inhibit contact welding, and being distributed through said alloy.
 6. A vacuum-type electric circuit interrupter comprising: a. an envelope evacuated to a pressure of 10 4 mm. of mercury or less, b. a pair of contacts within said envelope relatively movable into and out of engagement, c. said contacts being substantially free of absorbed gases and surface contaminants, d. at least one of said contacts having circuit-making and breaking regions formed of an alloy consisting essentially of a good-conductivity metal, beryllium, and a weld-inhibiting metal having substantially no solid-state solubility in the good conductivity metal or beryllium and having an effective freezing temperature below that of the good conductivity metal alloyed with beryllium, e. the beryllium being present in a quantity of between 2 and 19 percent by weight of the good conductivity metal beryllium alloy but in a quantity sufficiently low that a phase of said latter alloy other than intermetallic compound is present to impart effective machinability and resistance to cracking on closing impact, f. the weld-inhibiting metal being present in a quantity of less than about 5 percent by weight of the total alloy and in sufficient quantity to inhibit contact welding, and being distributed throughout said alloy. 